1. Field of the Invention
The present invention relates to an image processing device and image processing method used for a digital camera and the like.
2. Description of the Related Art
In recent years, the number of pixels of an image sensing element used in an image sensing device such as a digital camera is greatly increasing. The size of image data to be processed is also enormous. For this reason, a high-speed image processing device capable of shortening the time for image data processing is demanded.
As a technique for increasing the image data processing speed, a method using pipeline processing for image processing is known (Jpn. Pat. Appln. KOKAI Publication No. 2000-312327).
FIG. 1 is a block diagram showing the arrangement of a conventional image processing device.
A CPU 2 connected to a bus 1 causes a preprocess circuit section 3 to process an image sensing signal from a CCD image sensing element 30. The CPU 2 inputs the processed signal to an image processing section 5 through the bus 1. In the image processing section 5, image processing is performed as a pipeline scheme using a first image processing circuit section 5-1 to an nth image processing circuit section 5-n, which are connected in series. The image processing section 5 sends the processing result to a JPEG processing section 6. The JPEG processing section 6 compresses the image data by the JPEG scheme. The compressed image data is stored in a frame memory 4 through the bus 1 or recorded on a recording medium 32 such as a memory card through an interface 31.
According to this arrangement, data transfer through the bus 1 can be processed only by transfer from the frame memory 4 to the first image processing circuit section 5-1 and transfer from the JPEG processing section 6 to the frame memory 4. Hence, the data transfer size considerably decreases as compared to a conventional scheme that repeats data transfer between the frame memory 4 and each image processing circuit.
However, there is still a strong demand for higher-speed image data processing and shorter processing time in using the image processing device. To solve this problem, some conditions must be taken into consideration.
In the standard compression scheme, i.e., JPEG, processing such as compression is executed for each block called an MCU (Minimum Coded Unit). As an MCU, normally, 8×16 blocks, 16×16 blocks, or 8×8 blocks are used.
Hence, the image processing section 5 must segment image data into MCU blocks each having a predetermined size and transfer them to the JPEG processing section 6. In addition to this condition, the image processing section 5 must also transfer the segmented image data to the JPEG processing section 6 in a predetermined order. This condition is required to restore the data compressed by the JPEG processing section 6 to the original image data.
Even when an image recorded on a memory card or the like is to be read out and expanded by the JPEG processing section 6, higher-speed image data processing and shorter processing time are demanded.
Hence, to shorten the time of image data processing with compression or expansion in the image processing device, the above conditions must be satisfied, and the operation of the JPEG processing section 6 for compression or expansion must be guaranteed. Preferably, the measure taken has a form that does not change the operation of the JPEG processing section 6.